Several processes for the preparation of optically active phenethylamines are already known (cf. EP-A 0 341 475). In these processes, the racemic starting materials are resolved into the individual enantiomers by adding auxiliary reagents. In order to make these known processes for racemate resolution economical, the enantiomers which are in each case undesired must be racemized again and returned to the cycle.
In this connection, several methods have already been described which are suitable for racemizing enantiomers of phenethylamines which are not required. For example, optically active phenethylamines can be converted into the corresponding racemates by treatment with alkoxides in the presence of dimethyl sulphoxide (cf. EP-A 0 489 682). The process does, however, have the disadvantage that the alkoxides which are used as auxiliary reagents are relatively costly.
In addition, it has already been disclosed that racemic phenethylamines can be prepared by reacting optically active phenethylamines with acetophenone derivatives, then racemizing the resulting optically active Schiff bases using potassium tert-butoxide, and cleaving the resulting racemic Schiff bases using acids (cf. JP-A 07-188 120 and Derwent Abstract No. 95-290 356/38). A disadvantage of this process, however, is that the yields of the desired racemates are not always satisfactory. It is also unfavourable that the racemization requires potassium tert-butoxide, which is expensive.